1. Field of the Invention
This invention relates to a process for the direct preparation of 2-chloroterephthaloyl chloride by the controlled chlorination of terephthaloyl chloride in the absence of a solvent, using ferric chloride as a catalyst.
2. Description of the Prior Art
The literature generally teaches several ways of producing 2-chloroterephthaloyl chloride. For example, French patent 810,595 issued Mar. 24, 1937 discloses the conversion of chloroterephthalic acid to chloroterephthaloyl chloride using the reagent thionylchloride. U.S. Pat. No. 4,308,216 issued Dec. 29, 1981 discloses the phosgenation of an aromatic acid such as chloroterephthalic acid to chloroterephthaloyl chloride. The starting compounds for these methods, chloroterephthalic acid, and it's precursor chloro-p-xylene are not available in commercial quantities and limit the utility of these methods for some applications.
The direct chlorination of terephthaloyl chloride in a solution of chlorosulfonic acid containing sulfur trioxide and an iodine catalyst is taught in the preparation of 2,3,5,6-tetrachloroterephthaloyl chloride. The monochloro component of that process is only formed in very minor amounts. See example 1, table 1 of U.S. Pat. No. 3,833,652 issued Sept. 3, 1974 on the application of Knobloch.
The monochlorination of benzoyl chloride is described in the Journal of Chemical Society, Vol. 121, p.2510 (1922). In that process, a steady stream of thoroughly dried chlorine is bubbled through benzoyl chloride with a small quantity of anhydrous ferric chloride. Benzoyl chloride has only one functional acid chloride group and as such is readily converted to the monochloride. In the Journal of the American Chemical Society, Vol. 70, p. 3518(1948), isophthaloyl chloride was monochlorinated with ferric chloride catalyst at 95.degree. to 100.degree. C. and terephthaloyl chloride was chlorinated to the tetrachloro product. With isophthaloyl chloride, the first chlorine is substituted meta to both the acid chloride groups and the effect is to deactivate the ring further, thus high monochlorination is possible.
French patent 1,267,055 teaches ferric chloride as a chlorination catalyst in the preparation of dimethyl 2,3,5,6-tetrachloroterephthalate.